Get the plans to make your own Laser-cut Double-Folded Card Holder on your laser cutter.  It's recomended that you use 3-4oz vegetable tanned leather for the outter shell, though you can use a slightly lighter weight (2-3oz) leather for the inner piece and card slots to help reduce the overall bulk.
 
Black - cut lines for each of the card slots and the card holder body.
Blue - are the holes for sewing the wallet.  If you are going to hand punch the holes with your leather working tools, set these to ignore.